The present invention relates to magnetic recording medium that uses near-field optics in combination with nano-structure fine particles that contain a ferromagnetic metal. Further, the present invention relates to an information recording apparatus capable of recording huge amount of information and a method for reproducing information from such an information recording apparatus of huge storage capacity.
With increase in the amount of information handled in human society, recording density of recording media is increasing sharply in memory systems used for storing information. In the art of magnetic recording, recording capacity of the order of TB (terabytes)/inch2 is expected to be realized soon in the form of magnetic disks.
The amount of information of the world has already reached the order of exabytes (1018 bytes), and processing of information of this amount is expected to become the matter of everyday life by the decade of the year 2020 even for individual persons. In corresponding to this, it is expected that there should be realized the use of storage device of petabyte recording capacity having the recording density of 1 peta bpi by the latter half of the decade of the year 2020. In fact, there are already marketed home video recorders having the storage capacity of 1 terabytes in the year 2005, wherein this apparatus combines a HDD (hard disk drive) with DVD (digital versatile disk).
Thus, the foregoing prediction is thought not unrealistic as the prediction for the milestone twenty years later.
Judging from the recording time of 2 hours of current DVD recorders that record the information of 4.7 Gigabytes, the recording capacity of 1 petabyte should be the capacity capable of holding the pictures of whole life of one person of fifty years. Thus, by simple extrapolation of two-dimensional recording density from the current recording size of 25.4×25.4 nm2 realized for the case of the recording density of 1 tera bps, it is expected that the recording size should become 0.8×0.8 nm2 for the case of 1 peta bps, while this size corresponds to the size of only sixty four atoms of atomic diameter of 0.1 nm.
Thus, for achieving the recording density of 1 peta bpsi, nano-fabrication technology becomes the key, while development of nano-fabrication technology is in progress in the field of optical memories in relation to the use of near-field light. Thus, nano-technology is thought to become more and more important in this field. Further, associated with such development of nano-fabrication technology, development of new functional materials is also expected from novel nanostructures.
The technology of information recording is a comprehensive technology spanning over the extensive field of device technology, mechanics and system technology, and technological development has to be made by taking a balance between all these aspects. Arguments directed only to the materials or arguments directed only to the devices are not futile for developing the technology for practical application. Further, there is needed thorough and essential examination and breakthrough on the aspect of systems as to how to take out signals from a nanoscopic system to the macroscopic system. This includes breakthrough with regard to reproducing speed.
Thus, with the development of storage device of petabyte class, there are needed the elemental technologies of: high-sensitivity reading of information; electronic or electric-field reproducing of input light, stabilization of the state of minute regions, formation of nano-cells, prevention of migration, formation of protective layers, and the like, in terms of the conceptual technology. Further, there are needed elemental technologies of: miniaturization processing; pattern transfer; access control, and the like, in terms of the functional technology.
With the information recording medium of peta byte class, investigations should be made toward solid state construction of optical memories (as in the case of the information recording and reproducing apparatuses implemented in the form of semiconductor flash memories) by using nano-phonetic devices relying on the concept of nano-photonics, in combination with the technology of forming an integrated circuit. While semiconductor memories suffer from heating with increase of storage capacity, such a limitation imposed by heating can be overcome by integrating the semiconductor memory with a nano-photonic semiconductor memory that is operated by near-field light.
Toward materialization of the ultra-high density recording medium of petabyte class, investigations are being made for increasing the recording density to sub-peta bpsi by constructing a novel recording medium in anticipation of transition of the read/write technology to high spatial resolution and ultra high-speed, starting from the recoding medium having the recording density of super tera-bpsi, in which mono-domain magnetic crystal particles (spin nanocluster) free from magnetic domains that become the cause of noise or unstable operation, are aligned in order, and by decreasing the particle size step by step.
Ultimate goal is to attain further large capacity by controlling the spin of individual atoms based on the novel principle that uses photon-electron spin interaction.
So far, various information recording apparatuses and memory systems are developed such as semiconductor memories formed by semiconductor logic devices, magnetic memories such as magnetic disks, magnetic tapes, magnetic bubble memories, and the like, or optical media such as optical disks including Compact Disks and Digital Versatile Discs or optical cards. For a solid state magnetic memory, there is proposed a MRAM (magnetic random access memory). Reference should be made to Non-Patent Reference 1. Further, there is known the phenomenon of magnetic switching caused by spin transfer torque and there is proposed an MRAM that uses this principle (Non-Patent Reference 2).
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Matsuyama, K., Future Prospects and Technical Issues of Magnetic Random Access Memory (MRAM), Ouyou Buturi Vol.69, No.9, 2000, pp.1074-1079
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